Supercritical CO2 Extract from Microalga Tetradesmus obliquus: The Effect of High-Pressure Pre-Treatment.

High-pressure pre-treatment followed by supercritical carbon dioxide (ScCO2) extraction (300 bar, 40 °C) was applied for the attainment of the lipophilic fraction of microalga Tetradesmus obliquus. The chemical profile of supercritical extracts of T. obliquus was analyzed by ultra-high-performance liquid chromatography-high-resolution mass spectrometry with electrospray ionization (UHPLC-ESI-HRMS). Moreover, the impact of ScCO2 on the microbiological and metal profile of the biomass was monitored. The application of the pre-treatment increased the extraction yield approximately three-fold compared to the control. In the obtained extracts (control and pre-treated extracts), the identified components belonged to triacylglyceroles, fatty acid derivatives, diacylglycerophosphocholines and diacylglycerophosphoserines, pigments, terpenes, and steroids. Triacylglycerols (65%) were the most dominant group of compounds in the control extract. The pre-treatment decreased the percentage of triacylglycerols to 2%, while the abundance of fatty acid derivatives was significantly increased (82%). In addition, the pre-treatment led to an increase in the percentages of carotenoids, terpenoids, and steroids. Furthermore, it was determined that ScCO2 extraction reduced the number of microorganisms in the biomass. Considering its microbiological and metal profiles, the biomass after ScCO2 can potentially be used as a safe and important source of organic compounds.

Characterization and application of biochar-immobilized crude horseradish peroxidase for removal of phenol from water.

Biochar (BC) has attracted much attention as an environmentally friendly material for application in wastewater treatment. In this study, a suitability of wood-derived BC as a support for covalent immobilization of horseradish peroxidase (HRP) across glutaraldehide as crosslinker, known for the capability to remove phenol from water, was investigated. The efficiency of the immobilized HRP in removal of phenol (2 mM) from water at different reaction conditions (varying dosages of polyethylene glycol (PEG300) 0-750 mg/L; H2O2 1.5-3.5 mM, as well as reaction time 5-120 min) and the general toxicity of bio-treated water (Allium cepa test) were measured. All analyzes were performed for free enzyme as well. The immobilized enzyme showed the highest activity at temperature 30 °C and pH 7.0. The greatest efficiency of immobilized enzyme in phenol removing (90 %) was obtained by applying 2.5 mM H2O2 and 1.5 mg/L of PEG300 at pH 7.0 after 2 h of reaction period. After 4 washings, immobilized HRP retained more than 79 % activity with phenol removal of 64 %. Utilizing immobilized enzyme significantly reduces the toxicity of the tested water (80 %), which further suggested that it might be considered as an environmentally acceptable process for wastewater treatment. Possible degradation products remained in treated water were analyzed in water samples by liquid and gas chromatography with mass spectrometry, including also analysis of volatiles by solid phase microextraction technique; different phenol-base compounds were detected.

Adsorption mechanisms of chlorobenzenes and trifluralin on primary polyethylene microplastics in the aquatic environment.

Microplastics are ubiquitous in aqueous media, and the importance of considering their impact on the behaviour of other compounds in water has often been highlighted. This work thus investigates the adsorption mechanism of six priority substances (as defined by European Union legislation: trichlorobenzenes (1,2,3-TeCB, 1,3,5-TeCB, 1,2,4-TeCB), pentachlorobenzene (PeCB), hexachlorobenzene (HeCB), and trifluralin (TFL)) on primary polyethylene (PE) microplastics (polyethylene standard and polyethylene microparticles isolated from two personal care products) in Danube river water and a synthetic matrix. The maximum adsorbed amounts of the compounds investigated on PEs ranged from 227 µg/g for 1,2,3-TeCB to 333 µg/g for TFL. Equilibrium data was analysed using five isotherm models, with the best fit being described by the Langmuir model and the Dubinin-Radushkevich model indicating chemisorption as the likely sorption mechanism. In general, the Langmuir model showed that the investigated compounds will be better adsorbed on PEs in real river water, with the exception of 1,3,5-TeCB on all studied PEs, where the model predicts better sorption in the synthetic matrix. Compound characteristics and the polymer properties were the most important factors affecting the sorption process, while a significant matrix effect was also observed on PE behaviour. The fact that polyethylene particles derived from personal care products showed greater adsorption capacities than virgin PE demonstrates the necessity of investigating real-world PE samples when assessing the potential impact of MPs in the environment.

Fate of natural organic matter and oxidation/disinfection by-products formation at a full-scale drinking water treatment plant.

This paper investigates the fate of natural organic matter (NOM) during the full-scale drinking water treatment plant supplied by Danube river bank filtration. After the recent reconstruction of the plant, special attention was devoted to the effects of ozone dose and granulated activated carbon (GAC) filtration on the formation and behaviour of oxidation by-products (carbonyl compounds and bromate), as well as carbonaceous and nitrogenous chlorination by-products. For the oxidation of aromatic NOM moieties that absorb light at UV254, a lower ozone dose (1.0 g O3/m3) is sufficient, whereas to achieve a measurable reduction (about 20%) of total organic carbon, an ozone dose of 1.5 g O3/m3 is required. The content of carbonyl compounds in the water after ozonation increases relative to the content before oxidation treatment, and is up to 12 times higher in the case of aldehydes and up to 2 times higher in the case of carboxylic acids. Seasonal variations, including changes in temperature and the amount of precipitation, were also shown to affect the content of organic matter in the raw water, with slight effects on the quality of the treated water. In the winter, the organic matter content is slightly higher, meaning their transformation products aldehydes and carboxylic acids, are also higher during the winter than the summer.

Application of UV-activated persulfate and peroxymonosulfate processes for the degradation of 1,2,3-trichlorobenzene in different water matrices.

The presence of a large number of micropollutants in the environment, including priority and emerging substances, poses a significant risk to surface and groundwater quality. Among them, trichlorobenzenes are widely used in the syntheses of dyes, pesticides, solvents, and other chemicals and have been identified as priority pollutants by the European Water Framework Directive. The main goal of this study was to investigate the behavior of 1,2,3-trichlorobenzene (TCB) during the sulfate radical-based advanced oxidation processes (SR-AOPs) involving UV activation of persulfate or peroxymonosulfate (UV/S2O82- and UV/HSO5- processes). For this purpose, TCB was subjected to SR-AOPs in synthetic water matrices containing humic acids or hydrogencarbonate and natural water samples and a comparative evaluation of the degradation process was made. The toxicity of the oxidation by-products was also assessed. The evaluation of TCB degradation kinetics results using principal component analysis indicates that the efficacy of the SR-AOPs was highly dependent on the pH, initial oxidant concentration, UV fluence, and matrix characteristics. In natural waters, TCB degradation by the UV/S2O82- process proved to be most effective in acidic conditions (pH 5), while the UV/HSO5- process showed the highest efficacy in basic conditions (pH 9.5), achieving a maximum TCB degradations of 97-99%. The obtained results indicate that UV/S2O82- and UV/HSO5- as new generation oxidation processes have significant potential for TCB removal from water and result in only minor toxicity after treatment (14-23% of Vibrio fischeri bioluminescence inhibition).

The impact of humic acid on toxicity of individual herbicides and their mixtures to aquatic macrophytes.

This study investigates the impact of humic acid (HA) on the toxicity of selected herbicides and their binary mixtures to aquatic plants. The focus was on two auxin simulators (2,4-D and dicamba) and two photosynthetic inhibitors (atrazine and isoproturon). The results suggested that the addition of HA to the standard synthetic medium does not affect Lemna minor growth nor the toxicity of atrazine, but increases the toxicity of 2,4-D and the binary mixture of atrazine and 2,4-D. The addition of HA to the standard synthetic medium reversibly decreased the growth (biomass) of Myriophyllum aquaticum and enhanced the toxicity of individually tested herbicides (isoproturon and dicamba) as well as their binary mixture. The results showed delayed toxic effects of auxin simulators, especially 2,4-D in the Lemna test. The recovery after the exposure to individual photosystem II inhibitors (atrazine and isoproturon) is fast in both plant species, regardless of the presence of HA. In the case of selected mixtures (atrazine + 2,4-D and isoproturon + dicamba), recovery of both plant species was noted, while the efficiency depended on the herbicide concentration in the mixture rather than the presence or absence of HA.

Potential for anaerobic treatment of polluted sediment.

Due to the anaerobic nature of aquatic sediments, the anaerobic treatment of sediments utilizing already present microflora represents an interesting treatment option. Contaminated sediment can contain a variety of organic contaminants, with easily degradable organics usually present in the higher amounts, along with traces of specific organic pollutants (total petroleum hydrocarbons and polycyclic aromatic hydrocarbons). This study applies a comprehensive approach to contaminated sediment treatment which covers all the organic contaminants present in the sediment. The aim of this study was to (1) evaluate the anaerobic treatment of aquatic sediment highly loaded with easily degradable organics via determination of potential biogas and methane production, and (2) assess possibilities of using anaerobic treatment for the degradation of specific organic pollutants in order to reduce the risks posed by the sediment. In order to promote the methanogenic conditions of the indigenous microflora in the sediment, the addition of co-substrates acetate and glucose was investigated. The results, expressed as mL biogas produced per volatile solids content in sediment (VSadded) indicate that the addition of the co-substrate has a significant impact on biogas production potential (58.7 and 55.1 mL/g VSadded for acetate and glucose co-substrate addition respectively, and 14.6 mL/g VSadded for the treatment without co-substrate addition). Theoretical biochemical methane potential was assessed by Gompertz model and Chemical oxygen demand model. The Gompertz model fit better for all the applied treatments, and was capable of predicting the final productivity of biogas and methane in the first 30 days with a relative error of less than 14%. From the aspects of specific organic pollutants, total petroleum hydrocarbon degradation was promoted by co-substrate addition (degradations of 75% and 60% achieved by acetate and glucose co-substrate addition, compared to 45% for the treatment without co-substrate addition). Polycyclic aromatic hydrocarbons were reduced by significant amounts (84-87%) in all the applied treatments, but the addition of co-substrate did not further improve their degradation.

Response surface methodology investigation into the interactions between arsenic and humic acid in water during the coagulation process.

Interactions between arsenic and natural organic matter (NOM) are key limiting factors during the optimisation of drinking water treatment when significant amounts of both must be removed. This work uses Response Surface Methodology (RSM) to investigate how they interact during their simultaneous removal by iron chloride coagulation, using humic acid (HA) as a model NOM substance. Using a three factor Box-Behnken experimental design, As and HA removals were modelled, as well as a combined removal response. ANOVA results showed the significance of the coagulant dose for all three responses. At high initial arsenic concentrations (200µg/l), As removal was significantly hindered by the presence of HA. In contrast, the HA removal response was found to be largely independent of the initial As concentration, with the optimum coagulant dose increasing at increasing HA concentrations. The combined response was similar to the HA removal response, and the interactions evident are most interesting in terms of optimising treatment processes during the preparation of drinking water, highlighting the importance of utilizing RSM for such investigations. The combined response model was successfully validated with two different groundwaters used for drinking water supply in the Republic of Serbia, showing excellent agreement under similar experimental conditions.